Cumene is an important intermediate in the chemical and polymer industries, with global cumene production in 2006, being about twelve million metric tons and with global demand of cumene being expected to grow by more than 4% per year during 2006-2011.
The majority of all cumene manufactured in the world today is used for the production of phenol. The demand for phenol for the manufacture of Bisphenol-A and subsequently polycarbonates is accelerating, owing to the broadening applications of polycarbonates in the electronic, healthcare, and automobile industries.
Cumene is typically produced commercially by reacting benzene and propylene in complete liquid phase or mixed gas-liquid phase conditions in the presence of acid catalysts. Benzene feed in stoichiometric excess relative to the propylene feed is typically fed to the reactor to control or minimize the oligomerization of the propylene which subsequently causes coking and deactivation of the catalyst. Older processes based on solid phosphoric acid typically employ a benzene to propylene feed ratio of about 8:1, molar. The high benzene to propylene feed ratio employed in these processes is also needed to limit the production of polyisopropylbenzenes, mainly diisopropylbenzenes and triisopropylbenzenes, as the polyisopropylbenzenes produced over solid phosphoric acid (SPA) catalysts cannot be converted to cumene effectively and have to be used as gasoline blending stock and regarded as a process yield loss. The high benzene to propylene feed ratio also results in large amounts of unconverted benzene in the reactor effluent that needs to be recovered by distillation and recycled back to the reactor. Both of these factors make SPA processes uneconomical.
Several processes based on aluminum chloride catalysts, developed in the 1980s, have been able to reduce the feed benzene to propylene ratio to about 3:1, molar, thus reducing the capital and operating costs related to the recovery and recycle of excess benzene, and thus improved the process economics somewhat. Although more polyisopropylbenzenes are produced in the alkylation section of the aluminum chloride processes due to the lower benzene to propylene ratios, the polyisopropylbenzenes produced in these processes can be effectively transalkylated with benzene to produce additional cumene, and the overall process yield is improved significantly over those based on SPA catalysts. However, the introduction of aluminum chloride as catalyst into the cumene plant brings with it a host of environmental, plant maintenance, and plant and personnel safety issues due to the highly corrosive nature of the catalyst. As a result, only a few cumene plants based on the aluminum chloride processes have been built.
The introduction of zeolite catalysts based cumene technologies in the 1990s has revolutionized the cumene manufacturing industry. Zeolite catalysts are non-corrosive and environmentally benign. The use of zeolite catalysts thus eliminates the environmental, maintenance, and safety concerns related to the aluminum chloride catalysts. The zeolite based processes are able to produce cumene at higher product purity and process yield than those based on solid phosphoric acid. Most zeolite based technologies are able to effect alkylation at mild conditions and with feed benzene to propylene ratios between 6:1, and 3:1 molar, somewhat lower than those employed in processes based on solid phosphoric acid, while limiting propylene oligomerization and catalyst coking to achieve a catalyst cycle length of one to two years. More advanced zeolite based technology, such as the Mobil/Badger cumene technology licensed by Badger Licensing, are able to operate at extremely low benzene to propylene ratio of 2:1 molar or lower while achieving catalyst cycle lengths of five years or more. Although more polyisopropylbenzenes are produced at low benzene to propylene ratios, they can be very efficiently transalkylated with benzene to produce additional cumene, and their effect on overall process performance is negligible. Moreover, the significant reduction in the amount of unconverted benzene that has to be recovered by distillation and recycled to the reactor results in significant reductions in both capital investment and operating costs of the cumene plant.
The rapid growth of cumene, phenol and Bisphenol-A production, however, has caused some concerns related to the imbalance of the acetone byproduct produced from the phenol plant. Acetone and phenol are produced at an approximately 1:1, molar ratio from cumene, but are used at an approximately 1:2, molar ratio in the downstream Bisphenol-A production process. The excess acetone that is not used in the production of Bisphenol-A has caused some concern from phenol producers in that it may create a supply-demand imbalance and disrupt the economics of the phenol production business.
In addition, conventional phenol production is based on the use of propylene feedstock and the need to locate phenol plants near a source of propylene has become an important issue with producers. In today's olefins market, there is also a supply-demand imbalance in the supply of propylene produced from conventional sources such as ethylene plants due to the availability of feedstock that generally favor the production of propylene. This imbalance has forced phenol producers to build their plants closer to feedstock supplies rather than to product outlets.
Numerous research efforts have been directed at solving the acetone imbalance and propylene issues described above by recycling the excess acetone produced in the phenol plant to produce cumene. For example, U.S. Pat. No. 2,410,553, teaches an alkylation process in which benzene is reacted with acetone to form cumene in the presence of hydrogen and a zinc chloride catalyst. In addition, U.S. Pat. No. 2,412,230, teaches the production of cumene from benzene and isopropanol in the presence of a pyrophosphate of a metal selected from Group IB in the periodic table.
U.S. Pat. No. 5,015,786, teaches a process for preparing phenol, comprising the steps of: (a) alkylating benzene with isopropanol using a zeolite catalyst under liquid phase conditions to synthesize cumene, (b) oxidizing the cumene from step (a) with molecular oxygen into cumene hydroperoxide, (c) subjecting cumene hydroperoxide to acid cleavage to synthesize phenol and acetone, and (d) hydrogenating the acetone from step (c) with hydrogen gas under liquid phase conditions into isopropanol which is recycled to step (a).
U.S. Pat. No. 5,017,729, discloses a process for preparing phenol, comprising the steps of: (a) reacting benzene with propylene in the presence of an aluminum chloride complex to synthesize cumene, (b) oxidizing the cumene of step (a) with molecular oxygen to cumene hydroperoxide, (c) acid cleaving cumene hydroperoxide into phenol and acetone with an acidic compound, (d) hydrogenating the acetone of step (c) with hydrogen gas into isopropanol in the presence of a hydrogenation catalyst, (e) dehydrating the isopropanol of step (d) into propylene in the presence of an acidic compound, and (f) recycling the propylene of step (e) in a liquid state to step (a).
U.S. Pat. No. 5,160,497, discloses a process for producing phenol, comprising the following successive steps: (1) benzene is reacted in an alkylation step with a feedstock comprising propylene and isopropanol in the presence of dealuminized Y zeolite with an SiO2/Al2O3, molar ratio ranging from 8, to 70, to obtain a product which is fractionated to recover three fractions containing unconverted benzene, cumene, and polyisopropylbenzenes, respectively, (2) at least part of said polyisopropylbenzenes fraction is reacted with benzene in a transalkylation step by contacting a dealuminized Y zeolite with an SiO2/Al2O3 molar ratio ranging from 8, to 70, and cumene is collected, (3) the cumene obtained from steps (1) and (2) is oxidized with air to obtain cumene hydroperoxide which is cleaved with an acid to obtain a mixture of phenol and acetone, which mixture is then fractionated in order to separately collect phenol and acetone, and (4) the acetone obtained at the end of step (3) is at least partly hydrogenated into isopropanol that is then at least partly recycled directly to step (1).
U.S. Pat. No. 6,841,704, discloses a method for the preparation of cumene comprising reacting isopropanol or a mixture of isopropanol and propylene with benzene in presence of a beta zeolite catalyst having a SiO2/Al2O3 molar ratio greater than 10:1,, wherein the acidity of the catalyst is modified by surface addition of water, and wherein the isopropanol used is obtained by hydrogenation of acetone in at least two process stages.
EP 1,069,099, discloses a process in which benzene is alkylated with isopropanol or a mixture of isopropanol and propylene, under pressure and temperature conditions corresponding to complete gas phase of the mixture presence in the reaction section and in the presence of a catalyst comprising beta zeolite and an inorganic ligand.
U.S. Pat. No. 6,512,153, discloses a process in which benzene is reacted with isopropanol, alone or mixed with propylene, in the presence of a zeolite catalyst and under mixed gas-liquid phase, or complete liquid phase, at such temperature and pressure that the concentration of water in the reaction liquid phase is not higher than 8,000, ppm. The patent shows that the beta catalyst tested had adequate stability when the moisture level in the reaction liquid was maintained below 8,000, ppm. However, the catalyst deactivated significantly when the moisture content in reaction liquid exceeded 8,000, ppm.
Since the alkylation of isopropanol with benzene produces one mole of water for every mole of isopropanol consumed during the reaction, the restriction of 8,000, ppm water in the reaction liquid described in U.S. Pat. No. 6,512,153 posses a significant limit to the design of the reaction system. Such a 8,000, ppm restriction will require a very efficient removal of water within the reaction system and would require large process equipment, such as pumps, heat exchangers and decanter, and high energy consumption, resulting in high capital and operating costs and rendering such process uneconomical.
The 8,000, ppm limitation described in U.S. Pat. No. 6,512,153, also significantly limits the integration of phenol and cumene production, since it requires that the isopropanol feed to the alkylation reactor is substantially dry. In contrast, the crude acetone produced in a conventional phenol plant (in which cumene is oxidized with molecular oxygen to cumene hydroperoxide and then cleaved to acetone and phenol) typically contains 5-10, wt % of water. Hence this large amount of water will need to be removed, either before or after the acetone is converted to isopropanol, before the isopropanol can be fed to the isopropanol alkylation reactor. This is particularly crucial for optimizing an alkylation process in which low benzene to (propylene+isopropanol) ratio is desired, because in such a case, isopropanol will constitute a major fraction of the feedstock to the alkylation reactor and the 5-10% moisture that comes with isopropanol will make the moisture content in the reactor high, even before additional moisture is produced in the alkylation reaction. Since water is difficult to remove from acetone and isopropanol, reducing the water level in acetone and isopropanol involves significant capital investment and utility consumption. If the 8,000, ppm limit on water content in the alkylation reaction liquid can be expanded substantially or removed, significant savings in capital and utility costs can be realized
In accordance with the present invention, it has now been found that when an MCM-22, family molecular sieve is employed as the alkylation catalyst, benzene can be alkylated with isopropanol or a mixture of isopropanol and propylene in the presence of high levels of water in the feedstock without significant adverse affect on catalyst stability.